Artifacts when rendring QOpenGLWidget to QImage

gde23

Hello,

I have a QOpenGLWidget that I want to render to an png image.

This is my code (in a method of class derived from QOpenGLWIdget):

QSize size = QSize(scale*this->width(), scale*this->height());
QImage img = QImage(size, QImage::Format_RGB32);
QPainter painter(&img);
painter.setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
this->render(&painter);
img.save(filename);

Now the thing that I want to render e.g. looks like this.
As the screenshot taken from the GUI shows it looks like it should.

However when I want to save the exact same thing (using the code above) I get following:

So it seems that the regions where there is lots of specular reflections first get yellow, and if its even more then black.

Why is that?

nagesh

@gde23 Where is the drawing code? What is rendered to img through QPainter?

gde23

@nagesh : thanks for the answer however I dont thinkt it has to do we the opengl drawing code. Nothing special is happening there, just some triangles.

I found a solution/workaround myself:
Instead of rendering via QPainter there is a method in QOpenGLWidget that I didn't know existed:

QOpenGLWIdget::grabFramebuffer()

This woks for me and I can obtain the image without the artifacts. I still don't understand what went wrong in the first place, but anyway, that's fine.

nagesh

@gde23 good that you got the solution

Problem in earlier code might be because of
1)img is unintialized // fill with transparency
2)in order to take the screen shot , you are doing again drawing in img. rather than direct screen grab of window